Magnetic Flip-flop

The sensitivity of a reed switch can be affected by the judicious nearby placement of small magnets. Also, reed switches exhibit a certain amount of hysteresis: there is a distinct difference between the level to which the magnetic field strength must rise for the switch to pull in and the level to which it must fall for the switch to drop out. These properties in combination allow us to make an element with two stable states: a flip-flop.